Abstract
Basic Oxygen Furnace slag contains heavy metals, including vanadium, chromium and molybdenum. The leachability of these elements determines the industrial applicability of slag-based building products. This study investigates the post‑carbonation leaching of heavy metals from activated BOF slag pastes with the focus on the activator dosage and type (sodium and potassium citrate). Results reveal that the high degree of brownmillerite hydration boosts the leachability of heavy metals as its hydration product- hydrogarnet is less stable upon carbonation. With two leaching procedures, it is demonstrated that the carbonation resistance of pastes becomes the main attribute in preventing the leaching of heavy metals. It can be enhanced by optimising the activator dosage to facilitate the hydration of C2S and consequent structural densification.
Highlights
Current worldwide steel production reaches ~1.8 billion tons per year [1], among which about 2/3 is produced via the Basic Oxygen Steelmaking (BOS) process [2]
This study investigates the post‐carbonation leaching of heavy metals from activated Basic Oxygen Furnace (BOF) slag pastes with the focus on the activator dosage and type
The results demonstrate that the leaching of heavy metals from BOF slag pastes increases significantly after carbonation, mainly due to the decomposi tion of hydrogarnets and C-S-H gel
Summary
Current worldwide steel production reaches ~1.8 billion tons per year [1], among which about 2/3 is produced via the Basic Oxygen Steelmaking (BOS) process [2]. The chemical/mineralogical composition of BOF slag varies depending on the raw materials and process parameters used during the steel production It is generally represented by C2S, C3S, C2(A,F), RO phase (CaO-FeO-MgO-MnO solid solution, with the wuestite structure), and free CaO [7,8]. Cement and Concrete Research 148 (2021) 106534 activation process, the reaction of the most contaminated phasesbrownmillerite and belite takes place, resulting in the formation of siliceous hydrogarnet and C-S-H gel [10] These hydration products are known to reveal high capacities for heavy metals immobilisation. To account for the chemical and physical factors affecting the release of heavy metals, the leaching from unshaped and shaped slag pastes is analysed before and after carbonation in the context of reactivity of the slag phases, hydration products, carbonation resistance of pastes and compositional changes induced by the carbonation. Higher hydration degrees of C2S after 90 days of curing in pastes with 0.1 M and 0.2 M solutions of citrate salts than in pastes with more concentrated solutions lead to microstructural densification and conse quent improvement of the carbonation resistance
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